Hi. 

Working in an ageing retail environment there are a number of fire doors we are checking monthly/quarterly & maintaining where possible. A large number we have to assume are nominal as there is no certification. Gaps in the doors vary massively and I understand betweeen 2-4mm is only accepted, a large proportion haven been in situ for years and must of fitted within the regs way back when. Is it acceptable to test the doors as per the schedule and note where gaps are larger and await the fire risk assessment (4yearly) to advise if the door needs replacement. The RA company have advised that’s ok. 

Where can I get all useful and relevant information relating to fire doors gaps maintenance etc?

Never assume an old in situ door complied with the regulations of the day, the old fire door standard would not have usually had large gaps, there was no such thing as intumescent seals and a tight fit in a rebate was essential.

If you have excessive gaps then the door will not perform, there will (depending on the door location & what it's protecting) be a risk of serious harm and an offence may have been committed - waiting up to 4 years does not sound proportionate, plus if you are having a competent person inspect your fire doors they will tell you if it needs replacing as oppose to waiting for the risk assessor (who may not be a competent person for fire door inspection).

Advice sources: https://firedoors.bwf.org.uk/ & https://www.asdma.com/

Look here to see the reality about non conforming fire door installations: 

 

 

technically now if you haven't had appropriate training you should not be inspecting or undertaking any work on fire doors. if something goes wrong it will come back and bite you. they are really beginning to tighten this up after grenfell